Porous electrically-conductive gaskets have great value in use as seals for systems with special needs. These gaskets typically comprise a matrix of a non-conductive polymer to which electrically-conductive filler particles have been added and the mixture formed into a porous electrically-conductive composite material. The value of such gasketing materials lie in their ability to prevent or control buildup of electrical and electrostatic charges in a system or to control or prevent penetration of electromagnetic radiation from one side of the sealed system to the other by their electrically conductive nature, while at the same time providing lighter weight gaskets having high conformability to sealing surface irregularities, lower clamping force requirements, and the ability to provide controlled permeability from one side of the sealed system to the other by their porous nature.
Sealing requirements for these materials may vary depending on the use. They may be rigorous, where virtually all of the porosity of the gasket is removed under compression by the sealing surfaces thus providing liquid- or gas-tight seals, for example, in sealing chemical processing vessels, piping and equipment. They may also be used in less rigorous applications where lower compressive forces are applied and in which gasket porosity and permeability to liquids and gases are reduced only to minimally acceptable levels. For example, these may include seals for enclosures of chemical processing equipment, electrical and electronic equipment, analytical instruments and the like, for which there is a desire to permit pressure equilibration from one side of the sealed system to the other while excluding other influences of the ambient environment. In all cases, however, it is necessary that the gasket materials be electrically conductive when clamped in service.
When porous gasketing materials are clamped between metal surfaces they often stick to the surfaces when they are unclamped. This usually results in damage to the gasket material that makes it unsuitable for reuse and, in extreme cases, may result in damage to the metal sealing surfaces if the gasket must be scraped off in order to remove it from the metal sealing surface.
When a porous electrically-conductive gasket material is clamped between aluminum sealing surfaces there is a tendency for the high electrical conductivity between the aluminum sealing surfaces to be substantially reduced over a period of time. This tendency and the tendency to stick to surfaces are very undesirable in gasket materials.
It can be seen then that a porous electrically-conductive gasket material that releases easily from metal surfaces when unclamped and which permits easy removal or reuse would be very desirable.